The objective of this project is to understand the biochemistry and genetics of mitosis. We are using the simple eukaryote Aspergillus nidulans as a model system because it is easy to study morphologically and biochemically and its genetic system is among the best known of the simple eukaryotic organisms. Two sets of mutants are being studied. The first are the ts bim and nud mitotic mutants which were isolated in this laboratory and are blocked in mitosis and nuclear distribution respectively. The second are a set of benomyl/thiabendazole/oncodazole resistant mutants isolated by van Tuyl. The mitotic mutants are being characterized morphologically by electron microscopy and biochemically by two-dimensional gel electrophoresis. The tubulins of the drug-resistant mutants are also being studied in the two-dimensional gel system. The data indicate that benA, one three genes for benomyl resistance, is probably a structural gene for beta-tubulin.